1. Field of the Invention
The present invention relates to a digital television translator. More particularly, the present invention relates to a digital television translator that updates the program and system information protocol (PSIP) table with transmit (TX) channel data.
2. Discussion of the Related Art
Digital television (DTV) broadcasting systems are relatively new in the United States and offer many alternatives to traditional information and program distribution. In addition to traditional television programming, DTV systems offer the ability to distribute additional content in the form of data. This data can be any type of data including, for example, Internet data broadcast to one or more end users. Therefore, DTV broadcast systems offer great flexibility and diversity in the types of information they distribute. Like most conventional broadcast systems, DTV broadcast systems have a finite capacity limited by the bandwidth of its channels.
Additionally, as with other broadcast systems, such as analog television systems, the received DTV signal quality can vary greatly depending upon where the receiver is located. This problem is due to a number of adverse propagation effects such as multi-path, interference, and simple attenuation. One solution to this problem is to use multiple low power repeaters (On-Channel boosters) and/or translators (Re-modulators) to improve reception in areas of poor DTV signal reception. For example, a repeater, placed in an area of poor signal reception, receives a transmitted signal from a high power DTV transmitter and re-transmits an amplified duplicate signal at the same frequency. Translators, on the other hand, can receive a transmitted signal from a high power DTV transmitter and re-transmit the signal at a frequency different than the received frequency. Repeaters and translators are also used to extend the coverage of a broadcast system incrementally, and economically, to specific geographical regions.
FIG. 1 shows an example of a conventional DTV translator 1. The conventional DTV translator includes a down converter 2, a first local oscillator 3, an up converter 4, and a second local oscillator 5. A received DTV signal (RX RF input) is down converted to IF (intermediate frequency) by down converter 2. The IF is determined by the difference between the frequency LO1 generated by the first local oscillator 3 and the RF frequency of the received DTV signal (RX RF Input). The IF signal is then up converted to RF by up converter 4. The frequency of the up converted RF DTV signal (TX RF Output) is determined by the sum of the frequency LO2 generated by the second local oscillator 5 and the IF. The up converted DTV signal (TX RF Output) is then amplified and transmitted. With this arrangement, the transmitted signal contains the same information as the received signal, but is amplified. Further, when LO1=LO2, the transmit frequency is the same as the received frequency, and the apparatus operates as an on-channel booster. Alternatively, when LO1.noteq.LO2, the transmit frequency is different than the received frequency, and the apparatus operates as a translator.
In the DTV American Television Systems Committee (ASTC) standard, a DTV signal contains a Program and System Information Protocol (PSIP) table, which is a collection of hierarchically arranged sub-tables for describing system information and program guide data. One of sub-tables in the PSIP table is the Virtual Channel Table (VCT), which contains a list of attributes for virtual channels carried in the digital transport stream (baseband information). VCT fields “major channel number” and “minor channel number” are used for identification. The major channel number is used to group all channels that are to be identified as belonging to a particular broadcast corporation (or a particular identifying number such as channel “12”). The minor channel number specifies a particular channel within the group. The VCT also contains a “carrier frequency” field, which is used to identify the frequency at which the DTV signal is transmitted and received. As discussed herein, TX and RX channel data include at least one of the following major channel number, minor channel number, carrier frequency, and/or other data necessary for generating a proper DTV signal.
When a RF DTV signal is translated to a new frequency by the conventional DTV translator 1 of FIG. 1, the PSIP table no longer reflects the correct carrier frequency. In many DTV receivers, this discrepancy between the actual frequency of the received DTV signal and the carrier frequency data contained in the PSIP table prevents the receiver from properly receiving the DTV signal.
Also, a particular broadcast corporation may be assigned different major/minor channel numbers in geographical regions serviced by each translator. For example, Broadcast Corporation #1 could be assigned major/minor channel 12/04 in region #1 (served by a main DTV transmitter) and major/minor channel 37/04 in region #2 (served by a translator translating the main DTV transmitted signal). The conventional translator of FIG. 1 therefore generates a translated DTV signal that contains an incorrect channel number for transmission into region #2.
Moreover, in region #2, major minor/channel 12/04 may have already been assigned to Broadcast Corporation #2. In that case, a single DTV receiver in region #2 will receive two unique channels (Broadcast Corporation #1 and Broadcast Corporation #2) each having the same major/minor channel number in each of their PSIP tables. While some DTV receivers overcome these anomalies by allowing users to select whether to ignore PSIP data or to display the VCT information, other DTV receivers do not have this capability and are unable to properly tune to the program(s) of one or both of the two Broadcast Corporations.